1. Field of the Invention
This invention relates to a combustion system used in sooty smoke generating facilities such as a boiler equipment or a combustion furnace and more particularly to such combustion system provided with control means adapted to control the combustion system so that air polluting substances otherwise contained in exhaust gas generated from the boiler equipment or otherwise contained in exhaust gas generated from the combustion furnace usually used for incineration of general garbage or industrial waste may be effectively collected before emission into the atmosphere, and monitoring means adapted to detect an efficiency deterioration possibly occurring in a dust collector which functions, in turn, to catch and collect sooty dust contained in the exhaust gas from the combustion furnace.
2. Description of the Related Art
Exhaust gas generated from the facilities such as the boiler equipment and the combustion furnace contains sooty dust and the other various air polluting substances. Particularly the exhaust gas generated from urban garbage incinerators contains, in addition to carbon dioxide, water vapor and oxygen, various specified substances under the regulations such as soot and dust, hydrogen chloride (HCl), sulfur oxides (SO.sub.x) and nitrogen oxides (NO.sub.x). These substances are legally regulated, for example, by the Japanese Air Pollution Control Act with respect to its factors such as concentrations and total quantity of emission. The exhaust gas and/or sooty dust additionally contain various heavy metals such as cadmium, chromium and mercury, although they are present in extremely small quantities. Recently, a serious problem for the protection of environment has been posed by hydrogen fluoride (HF) and dioxins which are present in the exhaust gas although they are present also in extremely small quantities.
As for dioxins, the Japanese Ministry of Public Welfare laid down "Preventive guideline against generation of dioxins due to refuse disposal" from the viewpoint that it is desirable to minimize generation as well as emission of dioxins from these facilities into the environment. To prevent or at least minimize dioxins from being generated and emitted from garbage incinerating facilities in accordance with this guideline, addition of suitable neutralizer and/or adsorbent may be utilized or so-called dioxins decreasing condition including a combustion temperature (Temperature), a combustion time (Time) and a turbulence during combustion (Turbulence) in the incinerator may be adjusted depending on various factors such as a total quantity of generated dioxins.
To minimize generation of dioxins, the previously mentioned factors, particularly, the concentration and/or total quantity of dioxins which are being generated must be measured and thereby the current situation must be seized as accurately as possible. However, such measurement is difficult and requires a very expensive analyzer or the like, since the quantity of dioxins contained in the exhaust gas emitted into the atmosphere is extremely small. To solve this problem, it is well known, e.g., as described in Japanese Patent Application Disclosure Gazette No. 1992-161849, to utilize precursors of dioxins such as chlorobenzene and chlorophenol as substitute indices for the measurement.
According to this Patent Application Disclosure Gazette No. 1992-161849, after a quantity of the exhaust gas has been collected from the flue of garbage incinerating facilities, chlorobenzene sampling tube is taken out from the collector and the measurement is carried out using gas chromatography. Such a procedure of measurement necessarily takes a lot of time before the results of measurement can be reflected on the condition under which the operation of the incinerator should be operated.
In order to reflect the results of measurement on the operation of the incinerator, components contained in the exhaust gas must be continuously measured and, in view of this fact, Japanese Patent Application Disclosure Gazette No. 1993-312796 proposed a system for semi-continuous measurement/monitoring of chlorobenzene. However, this system is not adapted for direct measurement of dioxins but adapted for measurement of the substitute substances such as chlorobenzene on the basis of sample gas obtained by pretreating the exhaust gas so as to remove therefrom concomitant moisture and dust. Accordingly, there remains an apprehension that the results of measurement might be prevented from being rapidly and accurately reflected on the condition under which the incinerator should be operated.
On the other hand, the exhaust gas from the incinerator or the like has conventionally been guided to pass through various dust collectors before the exhaust gas is emitted into the atmosphere in order that the regulated substances and the other air polluting substances can be effectively collected from the exhaust gas before they are emitted into the atmosphere.
However, it becomes difficult to trap an adequate quantity of the air polluting substances as the dust collecting efficiency of the dust collector is deteriorated. To restore the desired dust collecting efficiency, cleaning and/or part-exchanging of the dust collector have usually been periodically carried out.
Conventionally, factors such as concentration of the regulated substances and the other air polluting substances contained in the exhaust gas have been detected and assessed according to the prescriptions by Japanese Industrial Standards to avoid the possibility that amounts of these undesirable substances higher than the critical values might be emitted. However, it is substantially impossible to perform detection and assessment in a continuous manner since detection and assessment also are performed on the basis of the sample gas having been subjected to the pretreatment suitable for every one of these substances as in the case of the previously mentioned measurement of chlorobenzene or the like. Consequently, the second best countermeasure has usually been adopted such that the sample gas is periodically collected from the flue and analyzed before the exhaust gas is emitted into the atmosphere.
If the result of measurement indicates that the air polluting substances contained in the sample gas exceed the respective standard values, such result may be sometimes due to an unexpected variation occurring in the condition under which the incinerator operates and/or the deteriorated efficiency of the dust collector. In this case, even if the dust collector is cleaned and/or the parts thereof are exchanged on the basis of measurement data, a certain quantity of the air polluting substances has already been emitted up to that time. In view of this fact, the cleaning of the dust collector and/or the exchange of parts thereof have usually been carried out independently of measurement of the sample gas and at the intervals of a sufficiently short period to minimize emission of the air polluting substances. As a consequence, the cleaning of the dust collector and/or the exchange of parts thereof must be frequently repeated. Frequent cleaning is time consuming and requires much labor, on one hand, and frequent exchange of parts correspondingly increases the maintenance cost.